1. Field of the Invention
The present invention relates to a transfer substrate, a transfer method, and an organic electroluminescent device manufacturing method and, more specifically, to a transfer substrate that is suitably used for patterning of an organic material layer, a transfer method using the transfer substrate, and an organic electroluminescent device manufacturing method.
2. Description of the Related Art
An organic electroluminescent device (hereinafter, referred to as organic EL device) utilizing electroluminescence of an organic material has been receiving attention as a luminescent device that is capable of high-brightness light emission by low-voltage direct drive. The organic EL device includes an organic layer being an accumulation of a hole transport layer and a luminescent layer between a lower electrode and an upper electrode.
A full-color display device of an exemplary type using such an organic EL device includes organic EL devices of various colors, i.e., R (red), G (green), and B (blue). These organic EL devices are disposed in an array on a substrate. In order to manufacture such a display device, there needs to form at least a luminescent layer through patterning on a luminescent device basis. The luminescent layer is the one made of an organic luminescent material that emits one color. Patterning of the luminescent layer includes shadow masking, ink jet, or others. With shadow masking, a luminescent material is applied to a sheet by vapor deposition or coating via an aperture-patterned mask, for example.
The issue here is that the patterning with such shadow masking has problems of a difficulty in finer patterning of the apertures formed to the mask, of a difficulty in patterning to areas of luminescent devices with high position accuracy if the mask is deformed in shape or increased in size, and others. Such problems increase the difficulty in finer patterning of organic EL devices and high-density designing. What is more, due to the exposure to the aperture-patterned mask, functional layers mainly including the previously-formed organic layer are susceptible to damages, and this is the cause of the reduction of the manufacturing yield.
The patterning with ink jet has the limits of patterning accuracy, thereby resulting in a difficulty in finer patterning of organic EL devices, high density designing, and size increase of substrates.
In consideration thereof, as a new patterning method for a luminescent layer configured by an organic material or any other functional layers, proposed is a transfer method using an energy source (heat source), i.e., thermal transfer. A display device using such thermal transfer is manufactured as below, for example. First of all, a substrate of a display device (hereinafter, referred to as device substrate) is formed thereon with a lower electrode. A separately-provided support substrate is formed thereon with a luminescent layer (transfer layer) via a light absorption layer for light-to-heat conversion. The result is a transfer substrate. The light absorption layer is exemplified by a pigment such as coloring agent or carbon, or a metal including nickel or titanium. The device substrate and the transfer substrate are so disposed that the luminescent layer faces the lower electrode. The resulting layer accumulation is exposed to a laser light from the side of the transfer substrate so that the luminescent layer is thermally transferred onto the lower electrode of the device substrate. At this time, through scanning of the layer accumulation with spot irradiation of the laser light, the luminescent layer is thermally transferred only to a predetermined area on the lower electrode. For more details, refer to Patent Document 1 (JP-A-2002-110350; paragraphs 0007 and 0081).
With thermal transfer, proposed is the configuration including a performance-increase layer above the luminescent layer. This is aimed not to cause luminescent layers to be turned off in or between processes that is often occurs due to adhesion and contamination of oxygen or water. The performance-increase layer includes a metal material such as alkali metal or an organic chemical reductant, and is formed above the luminescent layer by thermal vaporization, electron beam vaporization, or others. For more details, refer to Patent Document 2 (JP-A-2004-247309).